Conveying system for work pieces

ABSTRACT

A circuit-like system which includes a lower conveyor line, an upper conveyor line and a pair of lift or transfer mechanisms at the end of each line constructed for moving a work piece. A travel and hoist mechanism and a beam assembly are provided for discontinuously moving work pieces along the lower line and raising and lowering them for treatment. A hook assembly is provided for restraining the downward movement of a work piece at a selected location when the hook assembly is in an operative position. 
     The lift or transfer mechanism is provided which includes telescoping arms for grasping a work piece, which arms are carried by a vertically moveable carrier that is mounted in a stationary frame.

This application is a division of application Ser. No. 09/307,546 filedon May 7, 1999, and now U.S. Pat. No. 6,253,907

BACKGROUND OF THE INVENTION

This invention relates to a circuit-like conveying system whereby workpieces are moved to various treatment stations and more particularly toa system for moving the work pieces along a generally horizontal path ina discontinuous manner and vertically as required and to a relatedtransfer or lift mechanism.

Conveyors for moving work pieces from place to place or to treatmentstations are well known. One conveyor type moves work pieces from placeto place in a continuous manner. Another type of conveyor moves the workpieces in a start/stop or discontinuous manner so that the work piecescan be treated (usually dipped) at various stations. Such treatment mayinclude painting, plating, cleansing and the like. Conveyors of thistype move the work piece along a horizontal path, then the work piecemay be stopped, moved vertically downwardly at a given station so as todip the work piece in a treatment tank, upwardly out of the tank andthen back along the horizontal path. A transfer or lift mechanism,positioned at the end of the conveyor, is provided for moving the workpiece from one path or conveyor line to another. Conveyors of this typemay receive untreated pieces from a remote conveyor and deliver treatedpieces to the remote conveyor.

In a circuit-like conveying system there is provided a first or lowerhorizontal conveyor line or path along which the pieces are moved,stopped, lowered, treated, raised and moved to the end of the line. Atthe end of the line the pieces exit the first horizontal conveyor, areretrieved and moved vertically upwardly or delivered to the entrance toa second or upper horizontal line which may be a drying oven or dryingstation. The pieces are moved horizontally along a second or drying line(usually in an opposite direction to the first conveyor) to the exit ofthe second line and may be returned to the remote conveyor and anuntreated piece can be retrieved and delivered to the entrance for thefirst conveyor. This type of movement is seen in connection with platingmachines and the like and generally defines a circuit. Machines of thistype are known in the prior art but are believed to be complex andunreliable.

It is an object of this invention to provide an improved circuit-likeconveying system of the type described above which is less complex andmore reliable than machines of the prior art.

Systems of the type described herein include a transfer or lift stationat the exit end of the first line for retrieving treated pieces andmoving the pieces upwardly for delivery to the entrance to a secondconveyor line for drying or the like. A transfer station at the exit endof the second line is provided for removing dried pieces and deliveringthem to a remote conveyor. The transfer station or lift can alsoretrieve untreated pieces from the remote conveyor and move or deliverthem into the entrance end of the first treatment line. Transfer or liftmechanisms in the prior art tend to be complex, unreliable and notidentical at the respective ends of the lines.

It is an object of this invention to provide improved transfer stationsor lift mechanisms which are less complex, reliable and substantiallyidentical so that one can be placed at the end of the treatment line orthe drying line for the movement of work pieces.

With respect to the first conveyor, the work pieces are substantiallyequally spaced from one another and are moved downwardly as a group intotreatment tanks, treated, moved upwardly as a group and then moved on tothe next station for additional treatment.

It is an object of this invention to provide an improved system formoving the work pieces as a group a fixed distance, dipping them into aplurality of tanks for treatment, raising them and moving them on to thenext station.

These and other objects of this invention will become apparent from thefollowing description and appended claims.

SUMMARY OF THE INVENTION

There is p provided by this invention an improved circuit-like conveyingapparatus for the movement of work pieces between various treatmentstations an d a transfer station or a lift mechanism for retrieving workpieces from one conveyor and delivery to a second conveyor. Theapparatus includes a frame and a plurality of treatment stationspositioned relative to the frame. A travel mechanism carried on theframe is moveable relative to the frame between adjacent treatmentstations. A hoist mechanism, which is carried on the travel mechanism,cooperates in moving the work pieces between lower treatment and uppermovement positions. A beam, which cooperates with the hoist mechanism,extends along the frame and is connected to the hoist mechanism,preferably by an electrically driven retractable and extendablemechanism, carries or supports the work pieces and is constructed torelease work pieces when they are in treatment tanks. By thisconstruction a work piece can be releasably secured to the beam, loweredfor treatment, raised and moved horizontally from the entrance to theexit of the lower or treatment line. The work pieces are releasablysecured to the beam and are constructed to be released when positionedin a treatment station tank so that the beam can be moved rearwardly onestation and then raised so as to grasp a subsequent or trailing workpiece and move it forwardly to the next station. In this way the workpieces are moved from tank to tank.

A transfer station or lift apparatus for retrieving a work piece isprovided at the exit end of the conveyor or treatment line and isarranged to retrieve a work piece at the exit end and transport the workpiece to the entrance end of another conveyor which is horizontallydisposed above the first conveyor. The similar transfer apparatus orlift station is provided at the exit end of the upper conveyor formovement of a treated piece to a remote conveyor. The lift apparatus mayalso retrieve an untreated work piece from the remote conveyor andtransport it to the entrance end of the lower treatment conveyor.

In this way an untreated piece can be removed from the remote conveyor,moved to the first or treatment conveyor, then moved to the second ordrying conveyor and then retrieved from the drying conveyor and moved tothe remote conveyor. As is seen the apparatus provides a circuit-likesystem for movement of the work pieces as well as subassemblies such asthe travel mechanism, hoist mechanism and lift apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view showing a circuit-like conveyingapparatus which includes a first or lower treatment line, a second orupper drying line, lift mechanisms at the end of the lines andmechanisms for raising, lowering and moving work pieces in the lowertreatment line.

FIG. 2 is an end elevational view taken along line 2—2 of FIG. 1 showingthe conveying apparatus frame, the upper and lower lines and a treatmenttank positioned below the lower line.

FIG. 3 is a diagrammatic and perspective view showing work piecesassociated with a beam mechanism and positioned for lowering into aplurality of treatment tanks.

FIG. 4 is an end elevational view of a portion of the apparatus as seenin FIG. 2 showing a work piece positioned for lowering into a treatmenttank.

FIG. 5 is a view similar to FIG. 3 showing the support beam lowered andwork pieces lowered into a plurality of treatment tanks.

FIG. 6 is a view similar to FIG. 4 showing a work piece lowered into atreatment tank.

FIG. 7 is a view similar to FIG. 5 showing the work pieces in the tanksand the rearward movement of the support beam.

FIG. 8 is a view similar to FIG. 6 showing a work piece supported at thetop of the tank and the support beam free to move rearwardly.

FIG. 9 is a perspective view of a fragment of the beam, hanger and tankshowing the support beam moved downwardly and out of engagement with thehanger mechanism.

FIG. 10 is a perspective similar to FIG. 7 showing the support beamraised and the work pieces raised from the tank and the beam positionedto receive a new work piece.

FIG. 11 is a perspective view similar to FIG. 10 showing the supportbeam and work piece being moved forwardly so as to index the systemforwardly one unit.

FIG. 12 is a perspective and diagrammatic view of a circuit-likeconveying apparatus as in FIG. 1 and showing the travel and hoistmechanism for moving the support beam and lift mechanisms at the end ofthe conveyor lines.

FIG. 13 is a side elevational view of a portion of the lower conveyorshowing a hook mechanism for preventing the lowering of a work piece.

FIG. 14 is a side elevational view showing a piston-and-cylinderapparatus for operating the hook mechanism.

FIG. 15 is a perspective view showing the hook mechanism.

FIG. 16 is side elevational view showing the hook mechanism grasping awork piece.

FIG. 17 is a side elevational view showing the hook mechanism in anoperative position to restrain a first work piece and a second workpiece in a lowered position.

FIG. 18 is an exploded perspective view showing the support beam and thetravel and hoist mechanisms for causing the beam to index one stationand for raising and lowering the beam relative to the frame.

FIG. 19 is a diagrammatic and perspective view showing a pulley andcable system for operating the hoist mechanism and a chain system forraising and lowering the beam.

FIG. 20 is similar to FIG. 19 but with the hoist mechanism and beam inan extended position.

FIG. 21 is a plan view showing the travel and hoist mechanisms.

FIG. 22 is an elevational view showing the travel and hoist mechanismsconnected to the beam and taken along line 22—22 of FIG. 21.

FIG. 23 is a side elevational view of a traveler mechanism and takengenerally along lines 23—23 of FIG. 21.

FIG. 24 is a perspective view of a lift mechanism whereby work piecescan be retrieved from one conveyor and moved to a second conveyor.

FIG. 25 shows an arm and a saddle mechanism carried by the liftmechanism for engaging, supporting and moving a work piece and is takenalong line 25—25 of FIG. 24.

FIG. 26 is an end elevational view taken along line 26—26 of FIG. 24showing an arm or rail associated with the lift mechanism.

FIG. 27 is a side elevational view of the lift mechanism showing an armwith a work piece in various positions.

FIG. 28 is a plan-style view taken along line 28—28 of FIG. 27.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT I. The System Generally

Referring now to FIG. 1, there is shown a circuit-like conveying system10 generally which includes a lower or treatment conveying line 12generally, a lift or transfer mechanism 14 positioned at the end of thelower treatment line to retrieve work pieces therefrom. An upper ordrying conveying line 16 is provided to receive treated work pieces fromthe lift or transfer mechanism 14. A second lift mechanism 18 ispositioned at the end of the drying line 16 to retrieve dried workpieces therefrom and transfer those work pieces to a remote conveyor 20(see FIG. 12). Untreated work pieces can be moved from the remoteconveyor 20 to the entrance for the lower conveyor line 12. The workpieces are supported on a walking beam assembly 22 which is suspendedfrom a hoist mechanism 24 which cooperates with a travel mechanism 26that can be indexed forwardly one treatment station or backwardly onetreatment station.

The walking beam assembly 22, the hoist mechanism 24 and the travelmechanism 26 are interconnected, interrelated and work together totransport, raise and lower work pieces. However, in the descriptionherein the assembly 22 and mechanisms 24 and 26 may be described orreferred individually.

The conveying system 10 includes a stationary support frame 28 whichsupports the lower conveying line 12, the upper conveying line 16, thehoist mechanism 24 and the travel mechanism 26. As seen in FIG. 2, awork piece such as 30 is positioned above the treatment tank 32 forlowering into the tank 32 and subsequent treatment. It will also beappreciated that the circuit-like conveying system 10 has depth or isthree dimensional and accommodates aide work pieces such as 30. It isalso seen that the frame 28 spans a treatment tank such as 32.

The operation of the walking beam assembly 22 with respect to the workpieces and the hoist and travel operation is best seen in FIGS. 3-11inclusive. Referring to FIGS. 3, 5, 7, 10 and 11, the beam assembly 22includes a pair of spaced rails 22A and 22B. Associated with each railare L-shaped hanger engaging members such as 34. The beam assembly 22 israised and lowered by a plurality of chains such as 36. A work piecehanger such as 38 is arranged to support a depending work piece 40 andto engage the hanger engaging member such as 34. As seen in FIG. 3 workpieces such as 40, 42 and 44 can be suspended from the beam assembly 22over tanks such as 46, 48 and 50. Referring to FIG. 5, the beam assembly22 is lowered and the work pieces 40, 42 and 44 are immersed in tanks46, 48 and 50. The hangers such as 38 engage and rest on the side of thetanks and the hanger engaging members such as 34 are disengaged from thework pieces and can be moved to a position just below the hanger itself.

Then the beam 22 is no longer engaged with the hangers and can be movedrearwardly one station as suggested in FIG. 7. Then referring to FIG.10, the beam 22 is raised and as it is raised it engages the hangers forwork pieces 40, 42 and 44. But it will be noted that the rearward hangerengaging member is open (see FIG. 7) and can pick up a new work piecesuch as 52 in FIG. 10. Then the beam assembly 22 can be moved forwardlyas in FIG. 11 thereby indexing the work pieces one station forwardly. Itwill be noted that each station is spaced the same distance from anadjacent station.

Referring now to FIG. 4, the hanger 38 supporting the work piece 40 andhanger engaging member bracket 34 are seen. In FIG. 6 the hanger 38 islowered to rest on the edge of the tank such as 46 and the hangerengaging member 34 is shown in engagement with the hanger and the workpiece 40 is shown there below. As seen in FIG. 8. the hanger engagingmember 34 is positioned below and disengaged from the hanger 38 and isin position to be moved rearwardly with respect to the tank.

Referring to FIG. 9, the hanger 38 is shown as a square tube and thehanger engaging member 34 includes an angle iron 34A which is positionedto engage the hanger 38 and support the same. It is seen that based uponthe movement of the beam 22 downwardly, rearwardly, upwardly andforwardly the work pieces are moved in a rectangular pattern so as tomove the work piece from one tank to another.

FIG. 12 shows the entire circuit-like conveying apparatus 10 in adiagrammatic fashion. There the remote conveyor 20 and the liftmechanism 18 are shown whereby an untreated work piece can be removedfrom the conveyor 20, delivered to the lower conveyor line 12 onto thebeam assembly 22 so as to be moved to the treatment tanks, then moved tothe end of the conveyor 12 where the transfer mechanism 14 can retrievethe work piece and move it upwardly to the drying or upper conveyor 16.The upper conveyor 16 is a chain-like conveyor line that is positionedwithin an oven so as to form a drying line. Due to the heat to which thechain is exposed, the chain may lengthen and a take-up or tighteningmechanism is provided within the oven so as to adjust the chain.

Sometimes, it is desirable to prevent a work piece from being immersedor dipped in a particular tank. A hook assembly 50 is provided that issecured to a stationary structure 51 secured to the frame 28 (See FIGS.1 and 13-17). The hook assembly includes an inverted U-shaped frame 52that is secured to the stationary structure 51, two hingedly connecteddepending hooks 54 and 56 and an actuator bar 58 with an outwardlyextending arm 59 that connects the hooks 54 and 56 for joint movement. Apneumatic cylinder 60 is connected at one end to the frame section 52and at the other end to the actuator bar 58 via the arm 59. Byretracting the piston the bar is rotated and the hooks 54 and 56 raisedto a nonengaging position By extending the piston rod the hooks arerotated to a position so that when the other work pieces are lowered thehooks engage a hangar such as 62 and prevent or restrain the associatedwork pieces from being lowered. When the beam is raised for movement,the hooks can be rotated to an inoperative position and the previouslyrestrained work piece engages the appropriate support on the beam thework piece is moved to the next position and can be lowered and raisedthe other work pieces as seen in FIG. 17.

II. The Travel and Hoist Mechanisms and Beam Assembly

The interrelations and interconnections of the travel and hoistmechanisms 24 and 26 and the beam assembly 22 are seen in FIGS. 18-23inclusive. For purposes of description these mechanisms and assemblieshave been described separately.

Referring first to FIG. 18 the stationary frame 28 includes an endsection such as 70 and a pair of rails 72A and 72B. The travel mechanism26 and hoist mechanism 24 are associated with the frame 28. The beamassembly 22 supports the various hangers from the hoist mechanism by aplurality of spaced chains such as 74 and 76 and the previouslyidentified chain 36. The chains are spaced along the length of the beamso as to evenly raise and lower the beam. The chains are verticallyorientated but trained about a plurality of vertically orientatedsprockets such as 78 and 80 which are secured to the travel frame 82 androtate about a horizontal axis. The chains such as 74 and 76 are trainedabout the sprockets and are secured at their end to the pull rods 84 and86. The pull rods 84 and 86 are operated by a winch or spool 88 aboutwhich cables such as 90 and 92 are trained. A cable such as 90 passesthrough a set of pullies which permit it to retract the pull rods suchas 86. Those pullies include the horizontally arranged pulley 94, thepulley 96 and the pulley 98. It will be noted that the end of the cable90 is grounded or secured to the frame 82 at a point 100 similarly thepullies 94 and 96 are secured to brackets that are also grounded. Asseen in FIGS. 19 and 20 by winding the cables 90 and 92 about the drum88 the pull rods 84 and 86 are retracted and thus draw the frameassembly 22 upwardly through the action of the chains 74 and 76 andother chains which are connected to the pull rod and the assembly suchas 102 and 104. The frame 22 is shown in a lower position in FIG. 20 inwhich the drum 88 is reversed and the weight of the frame 22 tends topull the frame downwardly and coacts with the pull rods 84 and 86 andchains 74, 76, 102 and 104. The spool 88, cables 90, 92, rollers 94, 96,98 and grounding position 100 can also be seen in FIG. 21.

Referring to FIG. 22 the hoist mechanism 24, the travel mechanism 26 andthe beam assembly 22 is seen in elevational view and the beam assembly22 is in the upper position. As indicated above the entire beam assembly22 and take up apparatus can be indexed one station forwardly or onestation rearwardly so as to remove the work pieces from a first tank,raise them and move them to a second tank and then lower them Referringto FIG. 18, horizontal movement of the beam assembly 22 is controlled bythe travel motor 110, drive shafts such as 112, stops 114 and 116, andthe traveler or drive mechanism 118 generally (which is also seen inFIG. 23). Fundamentally the traveler 118 moves back and forth betweenthe stops 114 and 116 alone the chain 120. It is seen that with therespect to the traveler movement the chain 120 is trained about an idlersprocket 122, a driven sprocket 124 and another idler sprocket 126. Thusthe motor 110 rotates the drive shaft 112 which causes the sprocket 124to rotate. The chain 120 is drawn beneath the idler sprocket 122 overthe drive sprocket 124 and beneath the idler sprocket 126 to cause thetraveler mechanism 118 to move toward one of the stops 114 or 116. Itwill be appreciated that when the traveler mechanism moves the hoistmechanisms 24 similarly moves and so does the walking beam assembly 22.The mechanism is then reversed and the walking beam is moved to theother end at stop 114. At that point the beam 22 may be raised so as tolift the appropriate hangers and thus the work pieces have been indexedor moved one station forwardly.

III. The Transfer or Lift Mechanism

The transfer or lift mechanism can be seen in FIGS. 24-28 inclusive.However, reference is made to FIG. 12 where the lift mechanisms 14 and18 are shown at either end of the conveyor whereby work pieces can belied by a lift mechanism 14 from the end of the lower line 12 to theline 16. Other lift mechanisms can move dried work pieces from the upperline 16 to the remote conveyor 20 and from the remote conveyor 20untreated pieces can be removed and delivered to the lower conveyor 12.

Referring now to FIG. 24, a lift mechanism 150 generally is shown. Thelift includes a pair of side posts 152 and 154 which together with crossmembers 156 and 158 define a frame.

Within the frame there is provided a carrier 160 generally which can bemoved vertically upwardly or downwardly In the larger framed. A pair ofarm assemblies 162 and 164 are secured to the carrier and can moveinwardly or outwardly and from one side to the other side of the carrier160.

The carrier 160 includes an upper cross member 166 and a lower crossmember 168. A pair of vertical members 170 and 172 connect the crossmembers 166 and 168 and cooperate the posts 152 and 154 which have railstherein.

The carrier 160 is raised or lowered by a driven chain and counterweight mechanism. The drive motor 174 is connected via a shaft such as176 to chain drive sprockets 178 and 180 on the opposite sides of thelift. At the top of the lift mechanism idler sprockets 182 and 184 areprovided. Drive chains 186 and 188 are trained about the drive sprocketssuch as 178 and 180. The chain such as 186 is connected to the carrier160 by a bar such as 189. The chain 186 Is also connected to the counterweight 190 but on the opposite side of the chain. Thus the motor 174 candrive the chain so that the counter weight 190 moves upwardly, and thecarrier 160 via bar 189 descends. If the motor 174 is reversed thecounter weight 190 is moved downwardly and the carrier 160 is movedupwardly. Each of the arms 162 and 164 are secured to one of therail-like members 170 and 172 at a position spaced from the top crossmember 166 by brackets 171 and 173. Each of the arms includes astationary section such as 192 and a telescoping section such as 194.The telescoping section rides on a I-beam like rail 196 as seen in FIG.26. On each telescoping section such as 194 a hanger supporting saddlesuch as 198 or 199 is mounted. The carrier motor 200 and carrier driveshafts 202 and 204 cause the carrier chains 210 and 212 to rotate tocause the telescoping sections of the arms to move inwardly or outwardlyas seen in FIG. 24. It will be noted that the carrier cross member 166is spaced above the connection of the arm to the carrier so as to permitthe saddle 198 to move thereunder. Moreover, the entire carrier is sizedso as to permit clearance of a work piece suspended from saddles such as198 and 199. The carrier chain 212 is connected to the telescopingsection 194 by a pinion 213 and rack 214 which cooperate to cause thearm to move laterally inwardly and outwardly.

The saddle 198 is connected to one end of the telescoping section cable216. The cable 216 is trained about the idler 218 and secured to thetelescoping section at an end 220. The saddle 198 is also connected to asecond telescoping section cable 222 which is trained about a idler 224and connected to the telescoping section at end 226. Thus as the armmoves from one side of the carrier to the other side of the carrier itwill be seen that the saddle will move relative to the telescopingsection 194 and from one side of the carrier to the other side of thecarrier 160. This is seen in FIG. 27 where the stationary arm 192 andthe telescoping arm 194 are shown. In this situation a saddle such as198 is shown supporting a hanger such as 226 and work piece such as 228.It will be appreciated that the telescoping section 194 of the arm aswell as the hanger 226 and work piece 228 is moved from one side of thepost 152 and carrier 160 to the other side (i.e. left to right or viseversa). It is seen that in FIG. 27 the arm can be moved to a lowerposition or raised to an upper position and the saddle 198, hanger 226and work piece 228 can move accordingly.

IV. Operation

In operation an untreated work piece is delivered on a remote conveyor20 so that a lift mechanism such as 18 can position a telescopingsection such as 194 and hanger receiving saddles such as 198 and 199under the hanger for the work piece and thus remove the work piece fromthe remote conveyor. The hanger rests on the saddles and the section isretracted under the action of the drive motor 200. The telescopingsections of the arms are moved to the other side of the lift and inposition to be delivered to the treatment conveyor line such as 12.There the hanger and work piece are deposited on the hanger engagingbracket such as 34 associated with the beam 22 and the untreated piecesare added to the conveyor and moved as shown in FIGS. 3, 5, 7, 10 and11. The hoist and travel mechanisms 24 and 26 cause the untreated pieceto move into and out of the various treatment tanks and to the exit endof the lower line. At the exit end of the lower line 26 a lift mechanism14 is provided and arms on the lift mechanism are extended and engagethe hanger on the appropriate saddles. The arm is then retracted andlifted to the second line such as 16. There the arms extend and thehanger is deposited on the line 16. The treated piece is moved along thesecond or drying line to its exit end. There the lift mechanism 18extends the arms and engages the hanger using the saddles. The arms areretracted, moved to a lower position, and caused to move to the otherside of the lift mechanism and the hanger and work piece are depositedon the remote conveyor 20. The cycle is then repeated. It will beappreciated the appropriate controls are provided for the operation ofthe system

Numerous changes can be made to the embodiment disclosed herein withoutdeparting from the spirit and scope of this invention.

What is claimed is:
 1. A conveyor apparatus for the simultaneous anddiscontinuous movement of a plurality of work pieces to and between aplurality of treatment stations, said apparatus including: an elongatedand stationary structural frame having an entrance end and an exit end;a plurality of treatment stations positioned along the length of theframe and in spaced relation thereto; a travel mechanism carried on theframe and moveable relative to the frame between adjacent treatmentstations; a hoist mechanism carried on the travel mechanism and havingretractable and extendable members, and an elongated beam which extendsalong the frame, which is connected to the hoist mechanism by theretractable and extendable members and which is constructed for movementbetween a lower position and an upper position and to releasably supporteach of a plurality of work pieces; so that the beam can be lowered forthe work pieces to be treated moved one station towards the entranceend, raised and moved one station toward the exit end so as to move thework pieces forwardly one station.
 2. An apparatus as in claim 1 whereina hook assembly is mounted to the structural frame for engaging a workpiece and to prevent the work piece from being lowered with other workpieces on the beam, said hook assembly including a bracket mounted tothe frame, a pair of hook members hingedly mounted to the bracket and anactuator for moving the hook members between a grasping position and anon-grasping position.
 3. An apparatus as in claim 1 wherein saidstructural frame includes spaced stop members for limiting movement ofthe travel mechanism, and said travel mechanism includes a driveassembly for causing the travel mechanism to move between the stopmembers.
 4. An apparatus as in claim 3 wherein the drive assemblyincludes a traveler mechanism which includes a chain which extendsbetween stop members, a drive sprocket for engaging the chain, a drivemotor for rotating the drive sprocket and causing the travel mechanismto move along the chain between stop members.
 5. An apparatus as inclaim 1 wherein the retractable and extendable members include a pair ofelongated pull rods each extending along the frame, spaced andsubstantially parallel to each other, a spool member secured to thetravel mechanism, and a pulley and cable system connected to the spoolmember and to each of the pull rods so that winding of the cable aboutthe spool causes the pull rods to move in one direction and unwindingpermits the pull rods to move in the opposite direction.
 6. An apparatusas in claim 5 wherein a plurality of sprockets are mounted to the travelmechanism, and a plurality of support chains are provided, eachconnected at one end to the elongated beam and at the other end to apull rod and each trained about a sprocket so that the beam is raised orlowered by movement of the pulls rods.
 7. An apparatus as in claim 1wherein each beam includes work piece hangers or grasping elements forsupporting a work piece and for releasing a work piece for treatment. 8.A circuit-like conveyor system which includes: a lower conveyor linehaving an entrance and an exit end; a first lift mechanism positionedadjacent the exit end of the lower line; an upper conveyor line spacedfrom the lower line and having an entrance end and an exit end, with thefirst lift mechanism positioned adjacent the entrance end of the upperconveyor line; a second lift mechanism positioned adjacent the exit endof the upper line and the entrance end of the lower line; andconstructed for the simultaneous and discontinuous movement of aplurality of work pieces to and between a plurality of treatmentstations: an elongated and stationary frame; said plurality of treatmentstations positioned in spaced relation to the frame, and said lowerconveyor line; a travel mechanism carried on the frame and movablerelative to the frame between adjacent treatment stations; a hoistmechanism carried on the travel mechanism and having retractable andextendable supports; an elongated beam which extends along the frame andwhich is connected to the hoist mechanism by the retractable andextendable supports and which is constructed for movement between alower position and an upper position and to releasably engage each of aplurality of work pieces; and which is constructed for movement towardthe entrance end or toward the exit end of the lower conveyor so thatthe beam can be lowered and work pieces delivered to the treatmentstations; moved one station toward the entrance end of the lowerconveyor, raised, and moved one station toward the exit end so as tomove the work pieces forwardly one station; and wherein each of the liftmechanisms is constructed to retrieve a work piece on a hanger from afirst position and transport the work piece to a second verticallydifferent position, and each mechanism includes: a substantiallyvertical frame-like structure; a carrier assembly mounted in theframe-like structure for movement upwardly and downwardly and includes apair of generally horizontally positioned arm assemblies mounted to thecarrier, each of said arms including a section which is horizontallyextendable and retractable for movement toward and away from the carrierassembly; and a work piece receiving structure mounted to the extendableand retractable portion of each arm for movement with the arm to aposition toward the end thereof when the arm is extended from thecarrier.